1. Field of the Invention
The present invention relates to a piezoelectric device for converting an input mechanical quantity into an output electrical quantity, and vice versa.
2. Description of the Related Art
As generally known in the art, piezoelectric devices are typically used to convert an input mechanical stress into an output electric charge (voltage) and also to convert an input electric voltage into an output mechanical distortion. In the latter case, the output distortion can be used to generate mechanical force, displacement or vibration, and the device is sometimes called as an electrostrictive device. The term "piezoelectric device" as used herein is to be interpreted in its broadest sense, as encompassing an electrostrictive device as well. Similarly, the term "piezoelectric material" as used herein is to be interpreted in its broadest sense as encompassing an electrostrictive material as well.
Conventionally, piezoelectric devices have been used for detecting fine mechanical displacement or for adjusting lengths and/or positions of the optical path on a sub-micron order. There have been known unimorphor bimorph-type piezoelectric devices which serve to convert an electrical voltage into a bending or flexural deformation as actuators for ink jet printing heads, for example. In this instance, customers' or end users' requirements are oriented to a high-quality and high-speed printing performance, and it is desirable to realize an improved device with a minimized size and operability at a low driving voltage, which provides a satisfactory response characteristic and operational reliability.
Known unimorph- or bimorph-type piezoelectric devices typically include a first electrode layer, a piezoelectric layer and a second electrode layer which are sequentially laminated with each other. With such an arrangement of the piezoelectric layer and the electrode layers, it is important for the piezoelectric layer to have a dimension which is sufficient to cover the first electrode layer so as to avoid short-circuit between the first and second electrode layers and to assure a proper operation of the device. In this instance, however, when the piezoelectric layer has an edge which protrudes beyond the first electrode layer, the edge does not perform a piezoelectric function and may restrict the desired movement, relative to the substrate, of the remaining region of the piezoelectric layer which does perform the intended piezoelectric function. This is because the edge may be brought into a rigidly bonded state with the substrate due to chemical reaction or sintering caused by firing of the films for manufacturing the device. In other words, a rigidly bonded state between the substrate and the edge of the piezoelectric layer should be avoided in order to enable the piezoelectric layer to undergo an unrestricted movement and to achieve satisfactorily the intended functions. Therefore, it has been a conventional practice to adjust the dimension of the piezoelectric layer so that the edges of the piezoelectric layer are precisely aligned with those of the first electrode layer. Such an alignment requires a fine positioning of the relevant layers and leads to practical difficulty in realizing an improved productivity.